[RCC] my first two images! - Forums

Topic starter

Perfect post

Jun 1, 2021 · Edited: Jun 1, 2021

Hi everyone. I am just starting out on astrophotography, having been a visual observer for many years. I uploaded my first two attempts yesterday and would be grateful for your feedback.

Both were shot with my 20cm f/10 SCT and a 0.63 focal reducer mounted on a EQ6R Pro, using a Canon EOS 750D at ISO1600. As I am not guiding (not clever enough!) I kept the exposures to 15sec. Stacked with DSS and post in Photoshop.

I am thinking I don't have quite enough photons here, so I have two questions;

1. could I afford to go to 30sec subs without trailing (due to imperfect tracking and/or polar alignment)?
2. if not, would merely doubling the number of subs have the same effect? i.e. is it purely the total integration time that matters, or do you also need long individual exposures?

Thanks!

Well written Respectful Engaging

dkamen

Jun 1, 2021

Hi Stuart,

1. Maybe. I think at 1200mm you are already pushing it with 15 seconds, but no harm trying

2. You need to quadruple the number of subs to get an equivalent result in terms of signal to noise ratio.

All subs have the same read noise. A 30 second sub has two times the signal, so you get double SNR compared to the 15 second sub. On the other hand, 2x15 second subs averaged have sqrt(2) = 1.41 the SNR compared to the single 15 second sub.

You can probably get very nice boost in your SNR by increasing your working ISO to 3200 for the 15 second subs, based on DxOMark that's about 20% less read noise which is equivalent to using ~18 second subs. This is actually about the same as doubling the number of subs.

The above discussion assumes read noise is your main concern. There are other factors, for example the brightest parts of your image might burn at 30 seconds (or with the higher ISO).

Personally I think the images are exceptionally good for someone's first images, especially with such a large scope and unguided. Maybe a bit softer (particularly the first one) and greener than they should be but nothing tragic. For the softness, make sure your focusing is as tight as possible and the reducer at optimal distancing. Fixing the green is simply a matter of adjusting color balance and saturation levels in post processing, has nothing to do with your original data.

Cheers,
Dimitris

Helpful Supportive

Stuart Taylor

Topic starter

Perfect post

Jun 1, 2021 · Edited: Jun 1, 2021

Hi Stuart,

1. Maybe. I think at 1200mm you are already pushing it with 15 seconds, but no harm trying
2. You need to quadruple the number of subs to get an equivalent result in terms of signal to noise ratio.

All subs have the same read noise. A 30 second sub has two times the signal, so you get double SNR compared to the 15 second sub. On the other hand, 2x15 second subs averaged have sqrt(2) = 1.41 the SNR compared to the single 15 second sub.

You can probably get very nice boost in your SNR by increasing your working ISO to 3200 for the 15 second subs, based on DxOMark that's about 20% less read noise which is equivalent to using ~18 second subs. This is actually about the same as doubling the number of subs.

The above discussion assumes read noise is your main concern. There are other factors, for example the brightest parts of your image might burn at 30 seconds (or with the higher ISO).

Personally I think the images are exceptionally good for someone's first images, especially with such a large scope and unguided. Maybe a bit softer (particularly the first one) and greener than they should be but nothing tragic. For the softness, make sure your focusing is as tight as possible and the reducer at optimal distancing. Fixing the green is simply a matter of adjusting color balance and saturation levels in post processing, has nothing to do with your original data.

Cheers,
Dimitris

Thanks so much Dimitris! really helpful. I'm glad I am doing ok for a beginner

I'm going to try these targets again and use ISO3200 sticking w 15 sec and taking a few hundred subs.

As for focussing, I pointed at Arcturus and used a Bhatinov mask (as you need a nice bright star for that). Then I slewed to the targets without altering the focus knob. Could just slewing have altered the focus somehow?

Not sure what you mean about the reducer. I just screwed it on to the back of the telescope.

Stargazer66207

Jun 1, 2021

Stuart,
You are off to a GREAT start! Your images show good focus (which is one of the most important steps in getting good astro photos).
I would agree with Dimitris regarding trying to go to longer subs without guiding. I would suggest doubling your total integration time ( the total amount of time of your subs). Dimitris' comment regarding upping the ISO, but the success of that will be determined by whether or not it results in too much noise in your image.
You might want to consider guiding. There are a number of mine-guide scopes that would mount on your 8-inch SCT, and there are also packages (scope & guide camera) that are fairly reasonable. The PHD freeware is pretty much tried and true, and has a fairly gentle learning curve.
But, that being said, your images show that you are on the right track. Good work, and keep trying. You learn by doing!
Stargazer 66207

Helpful Respectful Engaging Supportive

Stuart Taylor

Topic starter

Perfect post

Jun 1, 2021 · Edited: Jun 1, 2021

Stuart,
You are off to a GREAT start! Your images show good focus (which is one of the most important steps in getting good astro photos).
I would agree with Dimitris regarding trying to go to longer subs without guiding. I would suggest doubling your total integration time ( the total amount of time of your subs). Dimitris' comment regarding upping the ISO, but the success of that will be determined by whether or not it results in too much noise in your image.
You might want to consider guiding. There are a number of mine-guide scopes that would mount on your 8-inch SCT, and there are also packages (scope & guide camera) that are fairly reasonable. The PHD freeware is pretty much tried and true, and has a fairly gentle learning curve.
But, that being said, your images show that you are on the right track. Good work, and keep trying. You learn by doing!
Stargazer 66207

Thanks for the positive feedback. You guys are really encouraging! These JPGs I posted are actually just screengrabs from photoshop (because it wouldn't let me save the TIFFs produced by DSS as JPGs for some reason). So the originals might look slightly better.

I will definitely consider guiding, but it looks really intimidating. So for now I'd prefer just to learn the craft step by step and get confident with the basic stuff.

I also have a faster scope on order, so I should be able to improve with that also

Respectful

Dale Penkala

Jun 2, 2021

Stuart Taylor:
Stuart,
You are off to a GREAT start! Your images show good focus (which is one of the most important steps in getting good astro photos).
I would agree with Dimitris regarding trying to go to longer subs without guiding. I would suggest doubling your total integration time ( the total amount of time of your subs). Dimitris' comment regarding upping the ISO, but the success of that will be determined by whether or not it results in too much noise in your image.
You might want to consider guiding. There are a number of mine-guide scopes that would mount on your 8-inch SCT, and there are also packages (scope & guide camera) that are fairly reasonable. The PHD freeware is pretty much tried and true, and has a fairly gentle learning curve.
But, that being said, your images show that you are on the right track. Good work, and keep trying. You learn by doing!
Stargazer 66207

Thanks for the positive feedback. You guys are really encouraging! These JPGs I posted are actually just screengrabs from photoshop (because it wouldn't let me save the TIFFs produced by DSS as JPGs for some reason). So the originals might look slightly better.

I will definitely consider guiding, but it looks really intimidating. So for now I'd prefer just to learn the craft step by step and get confident with the basic stuff.

I also have a faster scope on order, so I should be able to improve with that also

Hello Stuart,
I’m far from being “experienced here” but here are my thoughts for what they are worth.
I have to agree as well with longer exposure time. Don’t know what your gain is but that goes along with your ISO settings I believe.
As Dimitris mentioned color balance in the green channel will give you a more natural look.
And totally agree with Stargazer 66207 PHD 2 is as easy as it gets for auto guiding and in all honesty is quite easy to setup and get working. You will always want to try for better numbers but from my stand point if you have round stars leave it and go with your settings as is.
Personally I think your stars are very round and you could go after longer subs. Even going to 20 second’s I have found can make a difference the more subs you can get.

Dale

Supportive

Stuart Taylor

Topic starter

Perfect post

Jun 2, 2021

Dale Penkala:
Stuart Taylor:
Stuart,
You are off to a GREAT start! Your images show good focus (which is one of the most important steps in getting good astro photos).
I would agree with Dimitris regarding trying to go to longer subs without guiding. I would suggest doubling your total integration time ( the total amount of time of your subs). Dimitris' comment regarding upping the ISO, but the success of that will be determined by whether or not it results in too much noise in your image.
You might want to consider guiding. There are a number of mine-guide scopes that would mount on your 8-inch SCT, and there are also packages (scope & guide camera) that are fairly reasonable. The PHD freeware is pretty much tried and true, and has a fairly gentle learning curve.
But, that being said, your images show that you are on the right track. Good work, and keep trying. You learn by doing!
Stargazer 66207

Thanks for the positive feedback. You guys are really encouraging! These JPGs I posted are actually just screengrabs from photoshop (because it wouldn't let me save the TIFFs produced by DSS as JPGs for some reason). So the originals might look slightly better.

I will definitely consider guiding, but it looks really intimidating. So for now I'd prefer just to learn the craft step by step and get confident with the basic stuff.

I also have a faster scope on order, so I should be able to improve with that also

Hello Stuart,
I’m far from being “experienced here” but here are my thoughts for what they are worth.
I have to agree as well with longer exposure time. Don’t know what your gain is but that goes along with your ISO settings I believe.
As Dimitris mentioned color balance in the green channel will give you a more natural look.
And totally agree with Stargazer 66207 PHD 2 is as easy as it gets for auto guiding and in all honesty is quite easy to setup and get working. You will always want to try for better numbers but from my stand point if you have round stars leave it and go with your settings as is.
Personally I think your stars are very round and you could go after longer subs. Even going to 20 second’s I have found can make a difference the more subs you can get.

Dale

Thanks Dale. I am thinking that I'll go with both options next time - ISO3200 and 20 sec subs.

I will prob get around to guiding at some point, but I think I need a special scope piggybacked on the main scope for that. I don't have one of those at the moment. Just a finder scope (which I don't think will work)

Dale Penkala

Jun 2, 2021

Stuart Taylor:
Dale Penkala:
Stuart Taylor:
Stuart,
You are off to a GREAT start! Your images show good focus (which is one of the most important steps in getting good astro photos).
I would agree with Dimitris regarding trying to go to longer subs without guiding. I would suggest doubling your total integration time ( the total amount of time of your subs). Dimitris' comment regarding upping the ISO, but the success of that will be determined by whether or not it results in too much noise in your image.
You might want to consider guiding. There are a number of mine-guide scopes that would mount on your 8-inch SCT, and there are also packages (scope & guide camera) that are fairly reasonable. The PHD freeware is pretty much tried and true, and has a fairly gentle learning curve.
But, that being said, your images show that you are on the right track. Good work, and keep trying. You learn by doing!
Stargazer 66207

Thanks for the positive feedback. You guys are really encouraging! These JPGs I posted are actually just screengrabs from photoshop (because it wouldn't let me save the TIFFs produced by DSS as JPGs for some reason). So the originals might look slightly better.

I will definitely consider guiding, but it looks really intimidating. So for now I'd prefer just to learn the craft step by step and get confident with the basic stuff.

I also have a faster scope on order, so I should be able to improve with that also

Hello Stuart,
I’m far from being “experienced here” but here are my thoughts for what they are worth.
I have to agree as well with longer exposure time. Don’t know what your gain is but that goes along with your ISO settings I believe.
As Dimitris mentioned color balance in the green channel will give you a more natural look.
And totally agree with Stargazer 66207 PHD 2 is as easy as it gets for auto guiding and in all honesty is quite easy to setup and get working. You will always want to try for better numbers but from my stand point if you have round stars leave it and go with your settings as is.
Personally I think your stars are very round and you could go after longer subs. Even going to 20 second’s I have found can make a difference the more subs you can get.

Dale

Thanks Dale. I am thinking that I'll go with both options next time - ISO3200 and 20 sec subs.

I will prob get around to guiding at some point, but I think I need a special scope piggybacked on the main scope for that. I don't have one of those at the moment. Just a finder scope (which I don't think will work)

Dale Penkala

Jun 2, 2021

Dale Penkala:
Stuart Taylor:
Dale Penkala:
Stuart Taylor:
Stuart,
You are off to a GREAT start! Your images show good focus (which is one of the most important steps in getting good astro photos).
I would agree with Dimitris regarding trying to go to longer subs without guiding. I would suggest doubling your total integration time ( the total amount of time of your subs). Dimitris' comment regarding upping the ISO, but the success of that will be determined by whether or not it results in too much noise in your image.
You might want to consider guiding. There are a number of mine-guide scopes that would mount on your 8-inch SCT, and there are also packages (scope & guide camera) that are fairly reasonable. The PHD freeware is pretty much tried and true, and has a fairly gentle learning curve.
But, that being said, your images show that you are on the right track. Good work, and keep trying. You learn by doing!
Stargazer 66207

Thanks for the positive feedback. You guys are really encouraging! These JPGs I posted are actually just screengrabs from photoshop (because it wouldn't let me save the TIFFs produced by DSS as JPGs for some reason). So the originals might look slightly better.

I will definitely consider guiding, but it looks really intimidating. So for now I'd prefer just to learn the craft step by step and get confident with the basic stuff.

I also have a faster scope on order, so I should be able to improve with that also

Hello Stuart,
I’m far from being “experienced here” but here are my thoughts for what they are worth.
I have to agree as well with longer exposure time. Don’t know what your gain is but that goes along with your ISO settings I believe.
As Dimitris mentioned color balance in the green channel will give you a more natural look.
And totally agree with Stargazer 66207 PHD 2 is as easy as it gets for auto guiding and in all honesty is quite easy to setup and get working. You will always want to try for better numbers but from my stand point if you have round stars leave it and go with your settings as is.
Personally I think your stars are very round and you could go after longer subs. Even going to 20 second’s I have found can make a difference the more subs you can get.

Dale

Thanks Dale. I am thinking that I'll go with both options next time - ISO3200 and 20 sec subs.

I will prob get around to guiding at some point, but I think I need a special scope piggybacked on the main scope for that. I don't have one of those at the moment. Just a finder scope (which I don't think will work)

Yup I agree Stuart, baby steps thats how I did it.
You would need to run the numbers but sometimes just a 50mm will work for a guide scope. If your running around 2000mm fl on the imaging scope I would probably not want to use a guide scope without a fl of 300mm minimum. I’m sure others can give you a more accurate info that I can there.

I use my CF 80ed for my guide scope and its fl is 480mm.

Dale

Stuart Taylor

Topic starter

Perfect post

Jun 5, 2021 · Edited: Jun 5, 2021

Ok, so last night I tried the same two targets again, but with the following changes

slightly increased exposure times for the subs - 20sec
higher ISO - 3200
more subs - 94 on M13 and 112 on M57

M13 (2nd attempt)

M57 (second attempt)

I must say, I am finding the post processing very challenging. It's so incredibly arbitrary! You slide stuff about until you like how it looks, but it's hard to know if it bears any relation to reality! It seems more like an art project than anything scientific.

Engaging

Stargazer66207

Jun 5, 2021

Stuart,
Well done on your latest 2 images! I think they should be very satisfying to you. Re: your comment that post processing seems like an art project, YOU ARE EXACTLY CORRECT. Post processed images have little true scientific value. The intent is to make them visually satisfying. That is where the art comes in. If you browse the internet, you will see thousands of interpretations of the same deep sky object.
But, back to the subject. Looks like you are progressing nicely. Keep going!
Clear Skies,
Stargazer66207

Well written Insightful Respectful Concise Supportive

Stuart Taylor

Topic starter

Perfect post

Jun 5, 2021

Stuart,
Well done on your latest 2 images! I think they should be very satisfying to you. Re: your comment that post processing seems like an art project, YOU ARE EXACTLY CORRECT. Post processed images have little true scientific value. The intent is to make them visually satisfying. That is where the art comes in. If you browse the internet, you will see thousands of interpretations of the same deep sky object.
But, back to the subject. Looks like you are progressing nicely. Keep going!
Clear Skies,
Stargazer66207

Thank you! I appreciate that.

Dale Penkala

Jun 5, 2021

Stuart Taylor:
Ok, so last night I tried the same two targets again, but with the following changes

slightly increased exposure times for the subs - 20sec
higher ISO - 3200
more subs - 94 on M13 and 112 on M57

M13 (2nd attempt)

M57 (second attempt)

I must say, I am finding the post processing very challenging. It's so incredibly arbitrary! You slide stuff about until you like how it looks, but it's hard to know if it bears any relation to reality! It seems more like an art project than anything scientific.

Doing great Stuart!
I totally agree with you o the post processing! I’m struggling terribly my self with a couple of programs that I was told was SO EASY to use even a dummy can use them! Well evidently I’m worse then a DUMMY!
Keep up the good work and try to have fun which is really the most important thing!

Dale

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